Hello haskell-cafe, only for the souls interesting in writing efficient programs :) i included in this letter my own module used for fast variables - "DataVariables.hs". and "wc.hs" contains example of using these vars. DataVariables module contains many interesting beasts but for optimization purposes newVar/readVar/writeVar is especially interesting. these primitives mimics IORef interface, supports Int/Word/Bool variables, works in IO and ST monad and nevertheless they are compiled to the most-effective GHC primitives. moreover, they can be used outside GHC (of course, on other compilers just IORef/STRer are used to implement this) it was impossible to add Ptr's support with the same interface, so Ptrs supported by another functions - newPtr/readPtr/writePtr and don't work in ST monad. in other aspects fast Ptr variables are the same as fast general variables if you need to include these variables in data structures, use the types IntVar/WordVar/BoolVar/"MutPtr a" for the IO monad, and "MutInt s", "MutWord s", "MutBool s" for the ST monad another interesting beasts are unboxed Int and Bool values. although GHC can automatically unbox vars in some cases, using this module will guarantee unboxing. moreover, some operations such as bit shifts, are ineffective without explicit unboxing because their definitions don't use unboxed operations directly, but adds additional checks and conversions. using types FastInt and FastBool and associated operations guarantee unboxing on GHC and works on other compilers (where just boxed values are used to implement these types). one place from my lib where i used them to speed up program: putWord32be :: (Stream m h, Integral int, Bits int) => h -> int -> m () putWord32be h w = do let n = iUnbox (fromIntegral w) vPutByte h $! iBox ((n >># _ILIT 24) ) vPutByte h $! iBox ((n >># _ILIT 16) &# _ILIT 0xff) vPutByte h $! iBox ((n >># _ILIT 8) &# _ILIT 0xff) vPutByte h $! iBox ((n ) &# _ILIT 0xff) -- Best regards, Bulat mailto:bulatz@HotPOP.com